1) Field of the Invention
The invention relates to a clamping system for tools, in particular a clamping system for clamping tools in a press brake or fold-bending machine.
2) Description of the Prior Art
A press brake has an elongate lower beam and upper beam which are parallel to each other and can be moved toward and away from each other. Tools with which plate steel can for instance be bent are clamped in the lower beam and upper beam. By placing a steel plate between the tools of the upper beam and lower beam and moving the upper beam and lower beam toward each other the steel plate is pressed down between the tools and deformed so that a bending takes place which depends on the form of the tool.
In the prior art the clamping of such tools takes place, among other ways, by a mechanical clamping by means of clamp plates. Such a clamp plate is a plate which can be secured on the upper beam or lower beam by a bolt. The tool is placed between this clamp plate and the beam, after which the bolt is tightened and the tool is fixedly clamped. The clamping by means of clamp plates is a simple construction, but the clamping takes time since each bolt must be tightened manually.
Another frequently used clamping method is clamping of the tool with a hydraulically operated positioning pin. The positioning pin is arranged in the clamping beam and protrudes into the groove of the clamping beam into which the tool is placed. The clamping beam is normally mounted on an upper beam or lower beam of the press brake, or integrated therein. The upper beam and/or the lower beam is displaceable here toward the other beam. A hydraulic pressure unit is placed behind the positioning pin. This can be a hydraulic cylinder, although a better solution is a bellows. Once the tool has been arranged in the beam a hydraulic pressure is built up, whereby the positioning pin is pressed into the groove and thereby clamps the tool fixedly in the beam. A considerable hydraulic pressure is necessary in such a clamping construction, since the tool is clamped directly by the hydraulic pressure via the positioning pin. It is therefore usual to provide an external hydraulic unit for such clamping systems so as to enable a sufficient supply of hydraulic pressure. In the case of a hydraulically driven press it would be possible per se to envisage use being made of the hydraulic system of the press itself for the purpose of operating the clamping system. This is usually impractical however, since this hydraulic system operates at very high pressures and pressure peaks will moreover often occur during the pressing.
The positioning pin can further be provided on the end protruding into the groove with a chamfering which co-acts with an optionally truncated V-shaped positioning groove in the side surface of the tool. When the positioning pin is pressed into the groove of the beam the chamfering of the pin will be pressed into the positioning groove. Owing to the inclining contact surface the tool will on the one hand be clamped fixedly by the positioning pin, but on the other also be pressed upward so that the tool is properly clamped and positioned in the groove of the beam.
In order to prevent the tools from falling out of the clamping beam during insertion or release, the tools can be provided with a safety catch. This safety catch engages in a recess in the clamping beam. This recess is usually a horizontal groove in the clamping beam. The safety catch can be operated so that the safety catch can be retracted in order to place the tool vertically into the groove of the clamping beam, after which the safety catch is extended again and the ridge protrudes into a horizontal groove of the clamping beam.
When the safety catch cannot be operated, the tools will have to be inserted horizontally from the side of the beam. This is the case for instance in so-called American style tooling. The beam here has a groove with a T-shaped or reverse L-shaped cross-section. This T-shaped or reverse L-shaped groove is made up of the above stated vertical groove and the horizontal groove, into which the safety catch protrudes. An example hereof is shown in the older, U.S. Pat. No. 6,928,852 of applicant.
As described, it is usual to drive the positioning pin by means of hydraulics. The advantage of hydraulics is that a great force can thereby be generated. A hydraulic clamping system can moreover be controlled in simple manner by the control of the machine. A drawback however is that a separate hydraulic unit is necessary for the purpose of operating the clamping system. As stated, in the case of a hydraulically driven machine this functionality can optionally be provided by extending the hydraulic system of the machine. Such a combination of functions is of course not possible in the case the machine is for instance electrically driven.